Thermoplastic materials, such as hot melt adhesives, are used in a variety of applications including the manufacture of diapers, sanitary napkins, surgical drapes and various other products. The technology has evolved from the application of linear beads or fibers of material and other spray patterns, to air-assisted applications, such as spiral and melt-blown depositions of fibrous material.
Often, the applicators will include one or more dispensing modules for applying the intended deposition pattern. Many of these modules include valve components that permit the modules to operate in an on/off fashion. One example of this type of dispending module is disclosed in U.S. Pat. No. 6,089,413, assigned to the assignee of the present invention. The module includes valve structure which changes the module between on and off conditions relative to the dispensed material. In the off condition, the module enters a recirculating mode. In the recirculating mode, the module redirects the pressurized material from the liquid material inlet of the module to a recirculation outlet which, for example, leads back into a supply manifold and prevents the material from stagnating. Other modules and valves have also been used to provide selective metering and/or on/off control of material deposition.
Various dies or applicators have also been developed to provide the user with flexibility in dispensing material from a series of modules. For example, many dispensers are flexible with respect to the number of dispensing modules which can be mounted to the applicator for dispensing liquid material to a substrate. Additional flexibility may be provided by using different die tips or nozzles on the modules to permit a variety of deposition patterns across the applicator to be applied to the substrate. The most common types of air-assisted dies or nozzles include melt-blowing dies, spiral nozzles, and spray nozzles. Pressurized air is used to either draw down or attenuate the fiber diameter in a melt-blowing application, or to produce a particular deposition pattern. When using hot melt adhesives or other heated thermoplastic materials, the process air is typically heated so that it does not substantially cool the thermoplastic material prior to deposition on the substrate.
An exemplary applicator which permits additional flexibility by allowing users to tailor the applicator to specific needs is shown and described in U.S. Pat. No. 6,422,428, commonly assigned to the assignee of the present invention and hereby incorporated by reference in its entirety. This applicator comprises multiple manifold segments which may be selectively added or removed from the applicator to adjust the width of the liquid material dispensed from respective liquid dispensing modules secured to the individual manifolds segments.
In certain applications, it may be desired to use dispensing modules of different types to obtain varied patterns or forms of dispensed liquid material applied to a substrate. Spray applications may require different operating pressures for process air used to attenuate and control the pattern of dispensed liquid material when different modules are used on the same dispenser. In conventional applications however, the liquid dispenser is supplied by a single source of pressurized air and the manifold is not capable of receiving inputs from separately controlled pressure sources. Accordingly, when different types of liquid dispensing modules are used on a single dispenser, the process air pressure for the dispenser must be selected to work with all of the dispensing modules, therefore individual modules may not be receiving process air at a pressure that optimizes performance.
A need therefore exists for a liquid dispenser capable of providing selectively controlled pressurized air to individual modules used to dispense liquid material.